The 75166 is a twelve-aperture chopper wheel used with the 75160NF Oriel Optical Chopper Controller and LIDA-SRS-KIT Lock-in Digital Amplifier. The maximum beam size able to pass through the apertures is 0.43 inch [11 mm] diameter. The wheel is precision etched, and coated with a broadband absorber to minimize retroreflections. The chopper controller is used to adjust the chopping rate from 60 Hz to 800 Hz. This wheel is included at no extra cost with any order of the 75160NF or LIDA-SRS-KIT.